At my table Beate bought the contract as Mittelhand at 18, exchanged and played in clubs. She won the opening lead and started trumps from the top. Looking at all the hands we can see that the defence can bring home both the ace and the ten, but is this feasible in practice without risking throwing away a trump trick? (I was Vorhand. Had I held only two trumps I could have dropped DJ on the first round, telling partner he could drop HJ on the second. But as it was partner's HJ might have been doubleton, in which case I need to keep DJ.)

I don't think it's feasible in practice to save the trump A-10. You should not play the DJ on the first round of trumps for the reasons you gave. You can play it on the second round after partner plays the ace. In proactice, losing the CA does no harm on this hand because you can't win if Beate leads trumps from the top: she will only lose three tricks. The best you can do is get out of Schneider.